This invention relates to single or multi-stage centrifugal pumps having an inducer means operatively associated with the main impeller of a single stage pump or the first impeller of a multi-stage pump to improve the operating characteristics of such centrifugal pumps at low suction pressure, and more particularly the invention defines a centrifugal pump having a side or radially disposed inlet and radially disposed outlet wherein the inducer acts centripetally and turns the fluid from its transverse inlet direction to a substanially axial direction where it is directed into the suction inlet of the associated impeller.
The use of inducers in centrifugal pumps to aid and abet the operation thereof at low suctions pressures is an old and well known expedient.
Generally however such inducers have been applied to centrifugal pumps having a centrally disposed inlet for the fluid to be pumped. Other types of inducers for centrifugal pumps are shown in U.S. Pat. Nos. 2,395,704; 2,429,978; 2,985,108 and Italian Pat. No. 373,754.
None of these prior art inducers act both to improve the suction characteristics of the associated centrifugal pump and at the same time act to turn the fluid from an essentially radial entering flow direction to an axial exit flow direction at the outlet or trailing end of the inducer.
In Italian Pat. No. 373,574 the inducer has a plurality of radially disposed vane passages wherein both the inlet and the outlet for the vane passages are radially disposed. When the inducer is in assembled position in the pump, a spiral or scroll shape inlet passage for the pumps delivers the fluid being pumped to the inlet end of the radially extending vane passages. However, for reason of the vane passages having both an inlet and an outlet that is radially disposed, the inducer in Italian Pat. No. 373,574 does not function to turn the fluid flowing therethrough from the radially inward flow direction to the axial flow direction required for pumping the fluid into the suction eye of the associate impeller. In this patent the turning action on the fluid passing to the suction eye of the impeller takes place in the axially extending flow space in the central sections of the inducer and the space between the inducer and the suction eye of the associated impeller. Any turning action in this axially extending space is accompanied with violent turblance and mixing losses which adversely affect the suction characteristics of the impeller and the performance of the pump.